If they really are "anchors" at the end of each buried section you need not include all your subsystems in a single model as no information (F, x)traveling through these anchors.
But you can include disconnected models in a single analysis. After defining a new section, from the Input Menu click on Edit; from that menu you will see Global - click on that to reset the global coordinates of each subsystem. Also Alt-G or locate the tool button.
(By default, all new subsystems use the model origin (0,0,0) as the start point.)
But are they really anchors?